The only documentation I found is unclear if partial refunds are allowed and what information I would need to send in the request to accomplish this?
If you specify the full amount of the settlement transaction in the credit transaction or omit the amount element, a full refund occurs. To do a partial refund, specify the amount as something less that the full settlement. So, if the settlement was $100 and you want to refund $50, sent a credit transaction with <amount>5000</amount>.
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